The present invention relates to a motor-driven compressor and more particularly to a motor-driven compressor mounted on a vehicle.
Hybrid vehicle that is powered by both engine and electric motor varies the ratio of engine drive to motor drive in accordance with the running condition of the vehicle. In such a hybrid vehicle, if a compressor that operates a refrigeration cycle of an air conditioner is driven by the engine of the vehicle, the compressor cannot obtain necessary drive force constantly from the engine. In a hybrid vehicle, therefore, a compressor that is driven by electric power from a battery mounted on the vehicle is used. Such a motor-driven compressor is mounted on the body or engine of the vehicle.
The compressor is driven only by the electric motor when the engine is at a stop, such as during an idle stop. When the motor-driven compressor is driven with the engine at a stop, noise is developed due to the operation of the motor-driven compressor. Main cause of the noise development is the resonance due to the vibration of the body or engine caused by the vibration of the motor-driven compressor transmitted via its mounting rather than the sound radiated from the motor-driven compressor. Various mountings for a motor-driven compressor have been proposed to reduce the vibration transmission from the compressor to the body or engine of the vehicle.
Japanese Unexamined Utility Model Application Publication No. 64-44814 discloses a structure for mounting a compressor to an engine block or to mounting brackets of the engine by screws that are inserted through holes of the respective mountings formed integrally with the compressor and screwed into the threaded holes in the mounting brackets of the engine block. Two mountings are provided for each screw and each mounting has a rubber bushing press-fitted in the hole. Each rubber bushing has an outer cylindrical shell, an inner cylindrical shell and a rubber vibration isolator adhered between the outer and inner cylindrical shells. In addition, a spacer having the same inside diameter as the inner cylindrical shell is interposed between the two rubber bushings. Each screw is inserted through the first rubber bushing, the spacer and the second rubber bushing in this order and screwed into the threaded hole in the mounting bracket of the engine block. With the screw thus screwed in the threaded hole, the spacer prevents the first rubber bushing that is adjacent to the head of the screw from being deformed.
The structure in the above-referenced publication uses a large number of parts for mounting the compressor on the mounting brackets of the engine block and hence requires an extra assembling process for mounting the compressor to the mounting brackets of the engine block, thus increasing the manufacturing cost of the compressor. In addition, if the screw comes in contact with one end of the spacer in inserting the screw through the spacer, the screw may fail to be successfully inserted through the spacer. Therefore, it takes trouble to successfully insert the screw through the spacer, thereby increasing the manufacturing cost.
The present invention is directed to a motor-driven compressor which reduces the cost for mounting the compressor to an engine while reducing the noise development.